The rapid increase in digital data generated by advanced modalities and postprocessing packages is straining many image management systems. Radiology departments are seeking ways to maintain PACS performance in the face of network traffic jams, archive overload, and wide-ranging user requirements.

The introduction of multidetector CT and the consequent rise in demand for 3D image reconstruction had put considerable pressure on the PACS at Groningen University Hospital in the Netherlands, according to Peter van Ooijen, PACS manager. The radiology department upgraded its system to cope with the larger data flow and to ensure widespread availability of sophisticated image manipulation tools.

"More and more data are coming out of our CT nowadays," van Ooijen said. "There is also an increase in digital image resolution, in the number of images per acquisition, and in the use of 3D in radiology."

Evaluation of the radiology department's needs revealed four main tasks that the PACS should be able to accomplish:

• receive and store the large amount of digital data produced;
• respond rapidly to requests for data for postprocessing;
• store image reconstructions and display them on normal PACS viewers; and
• route selected image data via a Web server to network-based viewers.

Digital data workflow was divided into three activities: acquisition, storage, and evaluation. The acquisition stage encompassed generation of imaging data from modalities and from any immediate postprocessing. Project planners then calculated the monthly amount of MDCT data, which represented the greatest burden on the PACS, to ensure that the proposed storage solution would be adequate.

The chosen system consists of a central data distribution server linked to a DVD server and jukebox, five-year redundant array of inexpensive disks (RAID) for fast image retrieval, and four separate image providers delivering data to radiology review workstations.

A number of options have been integrated into the PACS for evaluation activities. To run 3D reconstructions, radiologists can use either thin-client software loaded onto a standard viewing workstation or a dedicated 3D workstation (Vitrea2) for advanced functionality.

The former option has the advantage of offering fast and easy 3D reconstruction during reporting, van Ooijen said. The PACS automatically transfers all CT and MRI data sets to the AquariusNET server, where they are stored locally for rapid retrieval.

Older data must still be requested from the archive, however, which takes longer. The number of concurrent users is limited by internal server memory and by the size of the data sets.

Imaging data are sent to a dedicated 3D workstation in response to a DICOM request initiated from that workstation or to a DICOM push from another workstation. The postprocessed images can either be written on a CD-ROM or sent back to the PACS for further distribution. All axial slices, original image series, and reconstructions can be transferred to a Web server in compressed format for review throughout the hospital.

Dr. Rudolf Mayrhofer, a radiologist at Danube Hospital in Vienna, also has witnessed the strain on PACS caused by digital modalities and larger image files. Danube Hospital has had a digital radiology department for more than 10 years, and it has upgraded its archive facilities many times to accommodate increased data flow.

Continual extensions to the PACS, including linking it to a new trauma center in 1998 and the purchase of digital angiography and fluoroscopy units in 1999, multiplied the amount of data being transferred within the network and stored in the short- and long-term archives. The next major challenge will be the integration of digital mammography.

"A single digital mammography study is 210 MB, so if you have 10 studies per day, one third of our expected daily digital workflow would be taken up with digital mammography," Mayrhofer said.

Radiologists at Danube Hospital also faced the task of transferring their long-term archive from optical disks to tape when manufacturers stopped supporting the old storage system. Austrian law dictates that medical records must be kept for 10 years, making the archive fairly sizable.

To compensate, data from groups of optical disks (160 per cycle) were copied to tape. A total of 14 hours per day was set aside to perform this data migration.

"We had estimated a migration time of six months," Mayrhofer said. "But in reality, it was not possible to do it in this way because the effects of the data migration on the network and the reaction time of the archive in copying data from one form of media to another were unacceptable."

The hospital implemented a revised plan to complete the data migration over a two-year period. The experience emphasized the need for upgrading networking capabilities as well as archive capacity.

The trend toward enterprise-wide archive solutions may ease the burden of continual archive maintenance and upgrades in the future, though this result remains to be seen, Mayrhofer said.